Accuracy, versatility, ease of use, durability, and cost of manufacturing are important parameters for wireless fluid pressure sensors. In the past hermetically sealed sensors have been used to provide a reference atmosphere for the pressure transducer (the pressure transducer providing an output indicative of a pressure differential on two surfaces of the transducer). A hermetic seal requires a container that is rigid and sealed well enough to withstand the normal wear and tear of a component which may be used in relatively instrument unfriendly industrial environments such as in chemical refineries and oil wells.
Such hermetically sealed pressure sensors provide a pressure measurement with respect to the environment inside the sensor package when the sensor was sealed. Therefore, it is critical for the sensor to maintain its hermetic seal to maintain correct operation. Since these sensors are generally placed in harsh environments that typically comprise corrosive gasses and/or liquids, the exterior housing of the sensor may become susceptible to corrosion over time. If the exterior housing were to degrade, in addition to contaminating the media being monitored, the sensor's hermetic seal maybe compromised resulting in a sensor that does not operate correctly.
To protect the sensor from its external environment, the exterior housing is generally composed of a material, such as stainless steel, that is resistant to corrosion. However, such corrosion resistant materials are generally not conducive to wireless transmission in the radio frequency range. In particular, materials such as stainless steel, which are generally resistant to corrosion from environments in which the sensor is typically positioned, do not typically allow for optimal transmission and reception of wireless signals. Therefore, to allow for improved transmission and reception of these wireless sensor signals, the exterior housing of the antenna portion of the sensor is generally composed of a polymeric material such as acrylonitrile butadiene styrene (ABS), whereas, the exterior housing of the remaining sensor body is generally composed of stainless steel. However, these polymeric materials that allow for wireless transmission are typically susceptible to corrosion and, therefore, not ideal for use in corrosive environments such as chemical refineries and oil wells.
What is needed therefore, is a protective covering that protects the fluid pressure sensor from corrosive environments. In addition to its corrosion resistance, the protective covering should also allow for optimal transmission and reception of wireless signals, particularly in the radio frequency range.